1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on the paper using an image forming unit such as an ink jet recording head, and a suction-type platen disposed at a position opposed to the image forming unit.
2. Description of the Related Art
Conventionally, in an ink jet recording apparatus for depositing ink ejected from nozzles of an ink jet recording head on a paper to form an image, a platen is disposed opposite to a nozzle face of the recording head. A pair of upstream transportation rollers on the upstream side of transportation (hereinafter simply referred to as the upstream side) and a pair of downstream transportation rollers on the downstream side of transportation (hereinafter simply referred to as the downstream side) are disposed to interpose a platen between them. Thereby, the paper is carried by both the roller pairs, which are intermittently driven to move the paper in the sub scanning direction (step feed). On the other hand, a carriage on which the recording head is mounted is moved in a main scanning direction to form an image for each predetermined area on the paper supported by the platen, while the intermittent movement is stopped.
By the way, when the ink is deposited on the paper from the ink jet recording head, the paper may be stretched and rippled (cockling) between the pair of upstream transportation rollers and the pair of downstream transportation rollers. As a result, a surface of the paper is in contact with the nozzle face to cause the recorded image to be contaminated, resulting in a lower image quality. Before a tip of the paper transported is carried by the pair of downstream transportation rollers, or after a trailing end of the paper is get out of the pair of upstream transportation rollers, if the paper is strongly curled, the leading or trailing edge of the paper is in contact with the nozzle face, resulting in a problem that the paper becomes dirty or the recording head is damaged.
In order to solve the above-mentioned problems, in JP-A-2001-213559, opening portions for paper suction having a rough rectangle shape in plan view are provided at regular intervals in a direction orthogonal to a transportation direction of a paper on a surface of a platen, and a suction unit for sucking air through the opening portions are provided.